Jer-Yen Yang

Leptin–STAT3–G9a Signaling Promotes Obesity-Mediated Breast Cancer Progression

Obesity has been linked to breast cancer progression but the underlying mechanisms remain obscure. Here we report how leptin, an obesity-associated adipokine, regulates a transcriptional pathway to silence a genetic program of epithelial homeostasis in breast cancer stem-like cells (CSC) that promotes malignant progression. Using genome-wide ChIP-seq and RNA expression profiling, we defined a role for activated STAT3 and G9a histone methyltransferase in epigenetic silencing of miR-200c, which promotes the formation of breast CSCs defined by elevated cell surface levels of the leptin receptor (OBR(hi)). Inhibiting the STAT3/G9a pathway restored expression of miR-200c, which in turn reversed the CSC phenotype to a more differentiated epithelial phenotype. In a rat model of breast cancer driven by diet-induced obesity, STAT3 blockade suppressed the CSC-like OBR(hi) population and abrogated tumor progression. Together, our results show how targeting STAT3-G9a signaling regulates CSC plasticity during obesity-related breast cancer progression, suggesting a novel therapeutic paradigm to suppress CSC pools and limit breast malignancy.

H3K9 Histone Methyltransferase, KMT1E/SETDB1, Cooperates with the SMAD2/3 Pathway to Suppress Lung Cancer Metastasis

Aberrant histone methylation is a frequent event during tumor development and progression. KMT1E (also known as SETDB1) is a histone H3K9 methyltransferase that contributes to epigenetic silencing of both oncogenes and tumor suppressor genes in cancer cells. In this report, we demonstrate that KMT1E acts as a metastasis suppressor that is strongly downregulated in highly metastatic lung cancer cells. Restoring KMT1E expression in this setting suppressed filopodia formation, migration, and invasive behavior. Conversely, loss of KMT1E in lung cancer cells with limited metastatic potential promoted migration in vitro and restored metastatic prowess in vivo. Mechanistic investigations indicated that KMT1E cooperates with the TGFβ-regulated complex SMAD2/3 to repress metastasis through ANXA2. Together, our findings defined an essential role for the KMT1E/SMAD2/3 repressor complex in TGFβ-mediated lung cancer metastasis.

AMP-Activated Protein Kinase Directly Phosphorylates and Destabilizes Hedgehog Pathway Transcription Factor GLI1 in Medulloblastoma

The Hedgehog (Hh) pathway regulates cell differentiation and proliferation during development by controlling the Gli transcription factors. Cell fate decisions and progression toward organ and tissue maturity must be coordinated, and how an energy sensor regulates the Hh pathway is not clear. AMP-activated protein kinase (AMPK) is an important sensor of energy stores and controls protein synthesis and other energy-intensive processes. AMPK is directly responsive to intracellular AMP levels, inhibiting a wide range of cell activities if ATP is low and AMP is high. Thus, AMPK can affect development by influencing protein synthesis and other processes needed for growth and differentiation. Activation of AMPK reduces GLI1 protein levels and stability, thus blocking Sonic-hedgehog-induced transcriptional activity. AMPK phosphorylates GLI1 at serines 102 and 408 and threonine 1074. Mutation of these three sites into alanine prevents phosphorylation by AMPK. This leads to increased GLI1 protein stability, transcriptional activity, and oncogenic potency.

UV-induced effects on toxicity of model disinfection byproducts

UV (Ultraviolet)-based treatment has been demonstrated to be effective for removal of some disinfection byproducts (DBPs) and to be beneficial for reduction of genotoxicity and cytotoxicity in chlorinated water. However, to a large extent, UV-induced effects on chemistry and toxicology have been treated as a black box, in the sense that little or no UV dose-dependent behavior has been reported. To address this issue, the effects of UV254 irradiation on 1,4-dibenzoquinone (BQ), 2,6-dichloro-1,4-benzoquinone (DCBQ), and chlorocreatinine (Cl-Cre) as model DBPs were examined, both in terms of photodegradation and cytotoxicity. These compounds have been identified as DBPs that are relevant in swimming pool settings; however, these compounds will be relevant in other water treatment settings, including drinking water production and wastewater reuse. UV254 irradiation was shown to promote photodecay of all three compounds. However, for BQ and DCBQ, the corresponding cytotoxicity of the UV-irradiated samples remained essentially unchanged, even when the compound was completely photodegraded. These results indicate that the photodegradation products of BQ and DCBQ carry similar cytotoxicity as their respective parent compounds. On the other hand, UV254-irradiation of Cl-Cre yielded a decrease in cytotoxicity that correlated with photodechlorination of Cl-Cre. These experiments also demonstrated a reduction in cytotoxicity in connection with photodechlorination of an N-chlorinated organic compound. Overall, the results of these experiments indicate the importance of defining products of UV photodecay processes, both in terms of chemistry and toxicity; these attributes are expected to be important in many UV-based applications, including potable water production, water reuse, and recreational water settings.

Evolutionary and developmental analysis reveals KANK genes were co-opted for vertebrate vascular development.

Gene co-option, usually after gene duplication, in the evolution of development is found to contribute to vertebrate morphological innovations, including the endothelium-based vascular system. Recently, a zebrafish kank gene was found expressed in the vascular vessel primordium, suggesting KANK genes are a component of the developmental tool kit for the vertebrate vascular system. However, how the KANK gene family is involved in vascular vessel development during evolution remains largely unknown. First, we analyzed the molecular evolution of the KANK genes in metazoan, and found that KANK1, KANK2, KANK3 and KANK4 emerged in the lineage of vertebrate, consistent with the two rounds of vertebrate whole-genome duplications (WGD). Moreover, KANK genes were further duplicated in teleosts through the bony-fish specific WGD, while only kank1 and kank4 duplicates were retained in some of the examined fish species. We also found all zebrafish kank genes, except kank1b, are primarily expressed during embryonic vascular development. Compared to invertebrate KANK gene expression in the central nervous system, the vascular expression of zebrafish kank genes suggested KANK genes were co-opted for vertebrate vascular development. Given the cellular roles of KANK genes, our results suggest that this co-option may facilitate the evolutionary origin of vertebrate vascular vessels.

KANK1 inhibits cell growth by inducing apoptosis through regulating CXXC5 in human malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNSTs) are a type of rare sarcomas with a poor prognosis due to its highly invasive nature and limited treatment options. Currently there is no targeted-cancer therapy for this type of malignancy. Thus, it is important to identify more cancer driver genes that may serve as targets of cancer therapy. Through comparative oncogenomics, we have found that KANK1 was a candidate tumor suppressor gene (TSG) for human MPNSTs. Although KANK1 is known as a cytoskeleton regulator, its tumorigenic function in MPNSTs remains largely unknown. In this study, we report that restoration of KANK1 in human MPNST cells inhibits cell growth both in human cell culture and xenograft mice by increasing apoptosis. Consistently, knockdown of KANK1 in neurofibroma cells promoted cell growth. Using RNA-seq analysis, we identified CXXC5 and other apoptosis-related genes, and demonstrated that CXXC5 is regulated by KANK1. Knockdown of CXXC5 was found to diminish KANK1-induced apoptosis in MPNST cells. Thus, KANK1 inhibits MPNST cell growth though CXXC5 mediated apoptosis. Our results suggest that KANK1 may function as a tumor suppressor in human MPNSTs, and thus it may be useful for targeted therapy.

New Insight into Cancer Aneuploidy in Zebrafish

Aneuploidy is one of the most common genetic alterations in cancer cell genomes. It greatly contributes to the heterogeneity of cancer cell genomes, and its roles in tumorigenesis are attracting more and more attentions. Zebrafish is emerging as a new genetic model for many human diseases including cancer. The zebrafish cancer model has shown an equivalent degree of aneuploidy as found in corresponding human cancers, thus it provides a great tool for us to study cancer aneuploidy and, in general, cancer biology. Here, we discuss some new advances of aneuploidy and the potential usages of this cancer model system.

Dual degradation signals destruct GLI1: AMPK inhibits GLI1 through β-TrCP-mediated proteasome degradation

Overexpression of the GLI1 gene has frequently been found in various cancer types, particularly in brain tumors, in which aberrant GLI1 induction promotes cancer cell growth. Therefore, identifying the molecular players controlling GLI1 expression is of clinical importance. Previously, we reported that AMPK directly phosphorylated and destabilized GLI1, resulting in the suppression of the Hedgehog signaling pathway. The current study not only demonstrates that AMPK inhibits GLI1 nuclear localization, but further reveals that β-TrCP plays an essential role in AMPK-induced GLI1 degradation. We found that activation of AMPK promotes the interaction between β-TrCP and GLI1, and induces β-TrCP-mediated GLI1-ubiquitination and degradation. Inhibiting AMPK activity results in the dissociation of the β-TrCP and GLI1 interaction, and diminishes β-TrCP-mediated-GLI1 ubiquitination and degradation. On GLI1, substitution of AMPK phosphorylation sites to aspartic acid (GLI13E) results in stronger binding affinity of GLI1 with β-TrCP, accompanied by enhanced GLI1 ubiquitination and later degradation. In contrast, the GLI1 alanine mutant (GLI13A) shows weaker binding with β-TrCP, which is accompanied by reduced β-TrCP-mediated ubiquitination and degradation. Together, these results demonstrate that AMPK regulates GLI1 interaction with β-TrCP by phosphorylating GLI1 and thus both post-translational modifications by AMPK and β-TrCP ultimately impact GLI1 degradation.

Phylooncogenomics: Examining the cancer genome in the context of vertebrate evolution.

Currently, human cancer genomics is making great progress, and many mutations of new cancer driver genes have been detected at an unprecedented rate in a variety of human cancers. Many details of the genetic alterations in cancer cell genomes have been revealed by the massively parallel sequencing. Long-lasting aneuploidy caused large-scale somatic copy number alterations remains a difficulty as there are too many genes located on such big chromosomal fragments, and this cannot simply be solved by increasing sequencing depth and tumor sample numbers. Comparative oncogenomics may provide us with a solution to this problem. Here, we review some of the common animal cancer models and propose to analyze cancer cell genomics in vertebrate phylogenetic backgrounds. Thus phylooncogenomics may provide us with a unique perspective on he nature of cancer biology unattainable by single species studies.

Identification of RECK as an evolutionarily conserved tumor suppressor gene for zebrafish malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNSTs) are a type of sarcoma with poor prognosis due to their complex genetic changes, invasive growth, and insensitivity to chemo- and radiotherapies. One of the most frequently lost chromosome arms in human MPNSTs is chromosome 9p. However, the cancer driver genes located on it remain largely unknown, except the tumor suppressor gene, p16 (INK4)/CDKN2A. Previously, we identified RECK as a tumor suppressor gene candidate on chromosome 9p using zebrafish-human comparative oncogenomics. In this study, we investigated the tumorigenesis of the reck gene using zebrafish genetic models in both tp53 and ribosomal protein gene mutation background. We also examined the biological effects of RECK gene restoration in human MPNST cell lines. These results provide the first genetic evidence that reck is a bona fide tumor suppressor gene for MPNSTs in zebrafish. In addition, restoration of the RECK gene in human MPNST cells leads to growth inhibition suggesting that the reactivation of RECK could serve as a potential therapeutic strategy for MPNSTs.